Calcium-based solid catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of catalyst preparation, and particularly relates to a calcium-based solid catalyst and a preparation method and application thereof. According to the preparation method, natural ore attapulgite is subjected to acid treatment, and calcium oxide is loaded by utilizing a high-quality pore structure and an excellent adsorption effect of the attapulgite, so that the cheap and efficient calcium-based solid catalyst is obtained and is used for catalyzing transesterification to prepare biodiesel. The calcium-based solid catalyst synthesized by the method disclosed by the invention has the advantages of abundant pores, stable structure, capability of being repeatedly used, mild reaction conditions, low cost, no corrosion to equipment and high biodiesel yield, and is expected to realize high value-added utilization of the attapulgite in biodiesel development.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a calcium-based solid catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The information disclosed in the background art of the present invention is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an admission or an indication in any form that this information constitutes the prior art that has become well-known to those of ordinary skill in the art.

[0003] As an environmentally friendly fuel, biodiesel is an ideal substitute for fossil fuels. Biodiesel has significant advantages such as being renewable, easily biodegradable, having low pollutant emissions during combustion, and having basically no greenhouse effect. Vigorously developing biodiesel has important strategic significance for sustainable economic development, promoting energy substitution, reducing environmental pressure, and controlling pollution. Currently, biodiesel is mainly produced by chemical methods, that is, transesterification reactions are carried out on animal and vegetable oils and fats and lower alcohols such as methanol or ethanol under alkaline catalysts to generate corresponding fatty acid methyl esters or ethyl esters, and then pure biodiesel is obtained through post-treatment operations such as purification.

[0004] Alkaline earth metal oxides are widely sourced and inexpensive, and are currently widely used solid base catalysts in biodiesel preparation. Among them, calcium oxide catalysts have the greatest development potential. Quicklime can be obtained by calcining limestone (mainly composed of CaCO3), and its main component is CaO. Calcium oxide is cheap, has strong alkalinity, and the basic sites are evenly distributed, and its solubility in methanol is very small, so it is used as a catalyst for preparing biodiesel. However, CaO also has problems such as being easily formed into colloids, the active components being easily lost, the catalytic yield being relatively low, the catalyst being difficult to recover, and being difficult to reuse; and the calcium-based catalysts obtained by traditional preparation processes have insufficient specific surface area (usually <20 m² / g) and single pore structure, resulting in poor dispersion of active components and easy sintering and agglomeration. Especially in continuous cycles, the activity rapidly decays due to structural collapse, making it difficult to meet the stringent requirements of industrial production for catalyst stability. Therefore, it is an urgent problem to prepare a calcium-based solid catalyst for biodiesel production with high activity, high biodiesel yield, strong stability, and cycle adaptability. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a calcium-based solid catalyst, a preparation method thereof, and an application thereof. When this catalyst is used for preparing biodiesel, it has high reaction activity, high biodiesel yield, simple separation of the catalyst and the product, and can be recycled.

[0006] To achieve the above object, the technical solution of the present invention is as follows: In the first aspect, the present invention provides a preparation method of a calcium-based solid catalyst, comprising the following steps: S1. Acid-treat the original attapulgite clay, filter, wash, and dry it to obtain acid-treated attapulgite clay. S2. Impregnate. Impregnate the calcium nitrate solution onto the acid-treated attapulgite clay to obtain a catalyst precursor. S3. Calcinate. Calcinate and activate the catalyst precursor to obtain a calcium-based solid catalyst.

[0007] In one or more embodiments, in step S1, the acid can be any one of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, dilute phosphoric acid, and dilute acetic acid, preferably dilute sulfuric acid.

[0008] In one or more embodiments, in step S1, the concentration of the acid solution is 2 - 4 mol / L, preferably 3 - 4 mol / L, and more preferably 3 mol / L.

[0009] In one or more embodiments, in step S1, the solid-liquid ratio of the original attapulgite clay to dilute sulfuric acid is 0.1 - 0.15 g / mL, preferably 0.1 g / mL.

[0010] In one or more embodiments, in step S1, the temperature of the acid treatment is 80 - 100 °C, preferably 90 °C; the time is 3 - 4 h, preferably 3 h.

[0011] In one or more embodiments, in step S1, the drying temperature is 105 - 110 °C, preferably 105 °C, and the time is 2 - 3 h, preferably 2 h.

[0012] In one or more embodiments, the mass ratio of calcium oxide prepared after calcination of calcium nitrate to the acid-treated attapulgite clay is 1.5 - 2.1:1. The mass ratio can be any value between 1.5 - 2.1:1, such as 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, preferably 1.8:1.

[0013] In one or more embodiments, in step S2, the impregnation temperature is 80 - 100 °C, preferably 90 °C; the time is 3 - 5 h, preferably 4 h.

[0014] In one or more embodiments, in step S3, the calcination temperature is 525 - 600 °C. The calcination temperature can be any temperature between 525 - 600 °C, such as 530 °C, 535 °C, 540 °C, 545 °C, 550 °C, 555 °C, 560 °C, 575 °C, 580 °C, 585 °C, 590 °C, 595 °C. The preferred calcination temperature is 550 °C; the calcination time is 1.5 - 2.5 h. The calcination time can be any value within 1.5 - 2.5 h, such as 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h. Preferably, it is 2 h. If the calcination temperature is too low, calcium nitrate in the catalyst cannot form CaO. If the calcination temperature is too high, grain migration intensifies, leading to aggregation of the active components, and due to particle sintering, the specific surface area decreases significantly, thus affecting the catalytic activity.

[0015] In one or more embodiments, the preparation method of the above-mentioned calcium-based solid catalyst specifically includes the following steps: S1: Prepare a dilute sulfuric acid solution, mix the original attapulgite clay with the dilute sulfuric acid solution, perform acid heat treatment in a water bath, and then filter, wash, and dry to obtain the acid-treated attapulgite clay.

[0016] S2: Mix calcium nitrate tetrahydrate and the acid-modified attapulgite clay solid in deionized water, and place it in a water bath for impregnation until the excess water evaporates.

[0017] S3: Place the obtained catalyst precursor in a muffle furnace for calcination activation to obtain the above-mentioned calcium-based solid catalyst.

[0018] In a second aspect, the present invention provides a calcium-based solid catalyst prepared by the method described in the first aspect.

[0019] In a third aspect, the present invention provides an application of the calcium-based solid catalyst prepared by the method described in the first aspect or the calcium-based solid catalyst described in the second aspect in the production of biodiesel.

[0020] The method for catalytically preparing biodiesel using the above-mentioned calcium-based solid catalyst includes the following steps: Alcohol can undergo a transesterification reaction with a raw material oil mixture such as palm oil, soybean oil, castor oil, etc. under the catalytic action of the above-mentioned calcium-based solid catalyst. It is preferred to use palm oil for the transesterification reaction.

[0021] The transesterification reaction is carried out with a molar ratio of alcohol to palm oil of 10:1 - 15:1, the addition amount of the catalyst is 3% - 7% of the mass of palm oil, the reaction temperature is 50 - 70 °C, the reaction time is 1 - 2 h. After the reaction, the mixture is separated to separate out the catalyst and crude biodiesel.

[0022] In one or more embodiments, the alcohol is selected from methanol or ethanol, preferably methanol.

[0023] In one or more embodiments, the molar ratio of the alcohol to the palm oil is 12:1 - 15:1, the addition amount of the catalyst is 5% - 7% of the mass of the palm oil, the reaction temperature is 65 - 70 °C, and the reaction time is 1.5 - 2 h.

[0024] In the transesterification reaction of methanol and palm oil, an excessive amount of methanol is usually used to shift the reaction equilibrium towards the product direction, improve the conversion rate. The excessive alcohol also helps to overcome the limitation of the reversible reaction and reduce the residue of intermediate products. However, if the amount of methanol is too high, the catalyst and palm oil will be diluted, resulting in a decrease in the effective adsorption effect of the catalyst, affecting the progress of the reaction, and thus reducing the yield of biodiesel. The yield can be relatively optimal within this range of catalyst dosage. If the catalyst dosage is too low, it will affect the reaction rate and conversion rate, etc., such as a significant decrease in the reaction rate, a decrease in the conversion rate, and the accumulation of intermediate products.

[0025] In one or more embodiments, the calcium-based solid catalyst can be reused after recovery. The specific steps are as follows: After the transesterification reaction is completed, the product and the catalyst are separated by centrifugation; subsequently, the catalyst is washed with n-hexane to remove the grease adsorbed on its surface; after drying the catalyst at 110 - 120 °C for 2 - 5 h, it is put into the next use.

[0026] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The attapulgite carrier of the present invention has good adsorption capacity and a large specific surface area. After acid treatment, more adsorption sites can be exposed, and CaO is evenly adsorbed on it. The obtained calcium-based solid catalyst has good structural stability, is easy to separate from the product after the catalytic reaction, and can catalyze the transesterification reaction multiple times. After being reused 5 times, the yield still remains above 88%.

[0027] (2) Attapulgite, as a natural ore, has a low cost. The calcium-based solid catalyst synthesized by the impregnation method has simple operation. When the biodiesel is produced by the catalyst synthesized by the present invention, it has a high catalytic reaction rate, a short reaction time, and does not require harsh conditions of high temperature and high pressure. The yield of biodiesel can reach 98.3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 Schematic diagram of the reaction route of the present invention; Figure 2 XRD characterization diagrams of the attapulgite before and after acid treatment and the catalysts obtained by calcining at different temperatures in Example 1 and Comparative Example 6 of the present invention; Figure 3 N2 adsorption characterization diagram, Figure 3 (a)-(d) are the N2 adsorption characterization diagrams of the attapulgite before and after acid treatment in Example 1 and Comparative Example 6, CaO prepared by the impregnation method, and the catalysts obtained by calcining at different temperatures. Detailed implementation manners

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0031] The technical solution of the present invention will be further described below in conjunction with specific embodiments. The present invention has no special restrictions on the sources of the reagents used in the following embodiments, and commercially available products well-known to those skilled in the art can be used.

[0032] Example 1 (1) Acid treatment of raw attapulgite Prepare a 3 mol / L dilute sulfuric acid solution, mix the raw attapulgite with the dilute sulfuric acid at a solid-liquid ratio of 0.1 g / mL, perform acid heat treatment in a water bath at 90 °C for 3 h, then filter and wash until neutral, and then place it in a blast drying oven at 105 °C for 2 h to obtain acid-modified attapulgite (denoted as H-ATP).

[0033] (2) Preparation of attapulgite-modified calcium-based solid catalyst Weigh 7.59 g of calcium nitrate tetrahydrate and 1 g of acid-treated attapulgite (the mass ratio of CaO:H-ATP is 1.8:1), add 100 mL of deionized water and mix. Stir for 4 h in a water bath at 90 °C to evaporate the water, and then place it in a muffle furnace and calcine at a heating rate of 5 °C / min at 550 °C for 2 h. Grind to obtain the attapulgite-modified calcium-based solid catalyst.

[0034] (3) Detection of catalytic transesterification activity The transesterification reaction was carried out using a microwave magnetic stirring reactor. Palm oil and methanol were used under the condition of an alcohol-to-oil molar ratio of 12:1. 0.75 g of attapulgite-modified calcium-based solid catalyst (5% of the mass of palm oil) was added, and the reaction was carried out at 64 °C for 120 min. After the reaction, the mixture was centrifuged to separate the catalyst and the crude biodiesel. The crude biodiesel was dried and then detected by gas chromatography. The yield of transesterified biodiesel was calculated to be 95.3%.

[0035] Comparative Example 1 (1) Acid treatment of raw attapulgite 3 mol / L dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, dilute phosphoric acid, and dilute acetic acid solutions were respectively prepared. The raw attapulgite and the acid solution were mixed at a solid-liquid ratio of 0.1 g / mL. At the same time, a pure water treatment control group was added. After acid heat treatment at 90 °C in a water bath for 3 h, it was filtered and washed to neutrality, and then placed in a forced-air drying oven at 105 °C for 2 h to obtain acid-modified attapulgite.

[0036] (2) Preparation of attapulgite-modified calcium-based solid catalyst 7.59 g of calcium nitrate tetrahydrate and 1 g of treated attapulgite (the mass ratio of CaO:H-ATP was 1.8:1) were respectively taken. At the same time, an untreated attapulgite control group was added. 100 mL of deionized water was added and mixed. Under the condition of a water bath at 90 °C, it was stirred for 4 h to evaporate the water, and then placed in a muffle furnace and calcined at 550 °C for 2 h at a heating rate of 5 °C / min. It was ground to obtain the attapulgite-modified calcium-based solid catalyst.

[0037] (3) Detection of catalytic transesterification activity The transesterification reaction was carried out using a microwave magnetic stirring reactor. Palm oil and methanol were used under the condition of an alcohol-to-oil molar ratio of 12:1. 0.75 g of attapulgite-modified calcium-based solid catalyst (5% of the mass of palm oil) was added, and the reaction was carried out at 64 °C for 120 min. After the reaction, the mixture was centrifuged to separate the catalyst and the crude biodiesel. The crude biodiesel was dried and then detected by gas chromatography. The yields of transesterified biodiesel were calculated to be 95.3% (pretreatment with dilute sulfuric acid), 93.4% (pretreatment with dilute hydrochloric acid), 93.2% (pretreatment with dilute nitric acid), 92.5% (pretreatment with dilute phosphoric acid), 88.9% (pretreatment with dilute acetic acid), 70.3% (pretreatment with water), and 3.6% (untreated), respectively.

[0038] Comparative Example 2 (1) Acid treatment of raw attapulgite Prepare a 3 mol / L dilute sulfuric acid solution, mix attapulgite raw soil with dilute sulfuric acid at a solid-liquid ratio of 0.1 g / mL, conduct acid heat treatment in a water bath at 90 °C for 3 h, then filter and wash until neutral, and then place it in a forced-air drying oven at 105 °C for 2 h to obtain acid-modified attapulgite.

[0039] (2)Preparation of attapulgite-modified calcium-based solid catalyst Weigh 7.59 g of calcium nitrate tetrahydrate and 1 g of acid-treated attapulgite (the mass ratio of CaO:H-ATP is 1.8:1), add 100 mL of deionized water and mix. Stir for 4 h in a water bath at 90 °C to evaporate the water, and then place it in a muffle furnace and calcine at a heating rate of 5 °C / min at 550 °C for 1.5 h and 2.5 h respectively. Grind to obtain attapulgite-modified calcium-based solid catalyst.

[0040] (3)Detection of catalytic transesterification activity Use a microwave magnetic stirring reactor to carry out the transesterification reaction. Use palm oil and methanol under the condition that the molar ratio of alcohol to oil is 12:1, add 0.75 g of attapulgite-modified calcium-based solid catalyst (accounting for 5% of the mass of palm oil), and react at 64 °C for 120 min. After the reaction, centrifuge the mixture to separate the catalyst and crude biodiesel. After drying the crude biodiesel, use gas chromatography to detect, and calculate that the transesterification biodiesel yields of the attapulgite-modified calcium-based solid catalysts prepared by calcining at 550 °C for 1.5 h and 2.5 h are 93.1% and 94.9% respectively.

[0041] Comparative Example 3 (1)Acid treatment of attapulgite raw soil Prepare 2 mol / L and 4 mol / L dilute sulfuric acid solutions respectively, mix attapulgite raw soil with dilute sulfuric acid at a solid-liquid ratio of 0.1 g / mL, conduct acid heat treatment in a water bath at 100 °C for 4 h, then filter and wash until neutral, and then place it in a forced-air drying oven at 105 °C for 2 h to obtain acid-modified attapulgite.

[0042] (2)Preparation of attapulgite-modified calcium-based solid catalyst Weigh 7.59 g of calcium nitrate tetrahydrate and 1 g of attapulgite treated with two different acid concentrations (the mass ratio of CaO:H-ATP is 1.8:1), add 100 mL of deionized water and mix. Stir for 4 h in a water bath at 90 °C to evaporate the water, and then place it in a muffle furnace and calcine at a heating rate of 5 °C / min at 550 °C for 2 h. Grind to obtain two attapulgite-modified calcium-based solid catalysts.

[0043] (3)Detection of catalytic transesterification activity The transesterification reaction was carried out using a microwave magnetic stirring reactor. Using palm oil and methanol under the condition that the molar ratio of alcohol to oil was 12:1, 0.75 g of attapulgite-modified calcium-based solid catalyst (5% of the mass of palm oil) was added, and the reaction was carried out at 64 °C for 120 min. After the reaction, the mixture was centrifuged to separate the catalyst and crude biodiesel. The crude biodiesel was dried and then detected by gas chromatography. The yields of transesterified biodiesel were calculated to be 76.7% and 93.4% respectively.

[0044] Comparative Example 4 (1)Acid treatment of raw attapulgite Prepare a 3 mol / L dilute sulfuric acid solution, mix the raw attapulgite and the dilute sulfuric acid at a solid-liquid ratio of 0.1 g / mL, carry out acid heat treatment in a water bath at 90 °C for 3 h, then filter and wash until neutral, and then place it in a forced-air drying oven at 105 °C for 2 h to obtain acid-modified attapulgite.

[0045] (2)Preparation of attapulgite-modified calcium-based solid catalyst Take 6.32 g of calcium nitrate tetrahydrate and 1 g of acid-treated attapulgite (the reduced mass ratio of CaO:H-ATP = 1.5:1) respectively, add 100 mL of deionized water and mix. Stir under the condition of a water bath at 90 °C for 4 h, and then place it in a muffle furnace and calcine at a heating rate of 5 °C / min at 550 °C for 2 h. Grind to obtain the attapulgite-modified calcium-based solid catalyst.

[0046] (3)Detection of catalytic transesterification activity The transesterification reaction was carried out using a microwave magnetic stirring reactor. Using palm oil and methanol under the condition that the molar ratio of alcohol to oil was 12:1, 0.75 g of attapulgite-modified calcium-based solid catalyst (5% of the mass of palm oil) was added, and the reaction was carried out at 64 °C for 120 min. After the reaction, the mixture was centrifuged to separate the catalyst and crude biodiesel. The crude biodiesel was dried and then detected by gas chromatography. The yield of biodiesel was 39.4%.

[0047] Comparative Example 5 (1)Acid treatment of raw attapulgite Prepare a 3 mol / L dilute sulfuric acid solution, mix the raw attapulgite and the dilute sulfuric acid at a solid-liquid ratio of 0.1 g / mL, carry out acid heat treatment in a water bath at 90 °C for 3 h, then filter and wash until neutral, and then place it in a forced-air drying oven at 105 °C for 2 h to obtain acid-modified attapulgite.

[0048] (2)Preparation of attapulgite-modified calcium-based solid catalyst 8.84 g of calcium nitrate tetrahydrate and 1 g of acid-treated attapulgite (the mass ratio of CaO:H-ATP is 2.1:1 in terms of converted mass) were respectively taken, added to 100 mL of deionized water and mixed. The mixture was stirred for 4 h under a water bath condition at 90 °C to evaporate the water, and then placed in a muffle furnace and calcined at 550 °C for 2 h at a heating rate of 5 °C / min. It was ground to obtain an attapulgite-modified calcium-based solid catalyst.

[0049] (3)Catalytic transesterification activity detection The transesterification reaction was carried out using a microwave magnetic stirring reactor. Using palm oil and methanol under the condition that the molar ratio of alcohol to oil was 12:1, 0.75 g of the attapulgite-modified calcium-based solid catalyst (accounting for 5% of the mass of palm oil) was added, and the reaction was carried out at 64 °C for 120 min. After the reaction, the mixture was centrifuged to separate the catalyst and the crude biodiesel. The crude biodiesel was dried and then detected by gas chromatography, and the yield of biodiesel was 93.8%.

[0050] Comparative Example 6 (1)Acid treatment of raw attapulgite A 3 mol / L dilute sulfuric acid solution was prepared, and raw attapulgite and the dilute sulfuric acid were mixed at a solid-liquid ratio of 0.1 g / mL. After acid heat treatment in a water bath at 90 °C for 3 h, it was filtered and washed to neutrality, and then placed in a forced-air drying oven and dried at 105 °C for 2 h to obtain acid-modified attapulgite.

[0051] (2)Preparation of attapulgite-modified calcium-based solid catalyst 7.59 g of calcium nitrate tetrahydrate and 1 g of acid-treated attapulgite (the mass ratio of CaO:H-ATP is 1.8:1 in terms of converted mass) were respectively taken, added to 100 mL of deionized water and mixed. The mixture was stirred for 4 h under a water bath condition at 90 °C to evaporate the water, and then placed in a muffle furnace and calcined at different temperatures of 500, 525, 575, and 600 °C for 2 h at a heating rate of 5 °C / min. It was ground to obtain attapulgite-modified calcium-based solid catalysts.

[0052] (3)Catalytic transesterification activity detection The transesterification reaction was carried out using a microwave magnetic stirring reactor. Using palm oil and methanol under the condition that the molar ratio of alcohol to oil was 12:1, 0.75 g of the attapulgite-modified calcium-based solid catalyst calcined at different temperatures was added (accounting for 5% of the mass of palm oil), and the reaction was carried out at 64 °C for 120 min. After the reaction, the mixture was centrifuged to separate the catalyst and the crude biodiesel. The crude biodiesel was dried and then detected by gas chromatography, and the yields of biodiesel were 2.1%, 57.5%, 92.8%, and 92.1% respectively.

[0053] Example 2 The catalyst obtained by the optimal preparation method optimizes the best transesterification reaction parameters through a neural network genetic algorithm.

[0054] The algorithm data selected the transesterification reaction parameter range as follows: the molar ratio of alcohol to oil was 3 - 15, the catalyst addition amount was 3% - 7%, and the reaction temperature was 60 - 68 °C. Seventeen groups of reaction parameters were set up, among which 11 groups were randomly selected as the training group, 4 groups as the verification group, and 2 groups as the test group. The predicted error was basically within 1%, the correlation coefficient reached above 0.93, and the predicted optimal reaction parameters were an alcohol - to - oil molar ratio of 14, a catalyst addition amount of 6.7%, and a reaction temperature of 67 °C, with a biodiesel yield of 98.4%. Under these optimal reaction parameters, a transesterification experiment was carried out for verification, and the measured biodiesel yield was 98.1%.

[0055] Example 3 Repeatability experiments of attapulgite - modified calcium - based solid catalyst were carried out with the optimal reaction parameters determined in Example 2. After each transesterification reaction ended, first, the product and the catalyst were separated by centrifugation; then, the catalyst was washed with n - hexane to remove the adsorbed grease on its surface; finally, the catalyst was placed in a vacuum drying oven and dried at 110 °C before being put into the next use. After being reused 5 times, the biodiesel yield corresponding to the attapulgite - modified calcium - based solid catalyst could still be maintained at 88.4%.

[0056] The reuse yields of the attapulgite - modified calcium - based solid catalyst under the same conditions are shown in Table 1.

[0057] Repeatability experiments of the CaO catalyst (obtained by calcining calcium nitrate tetrahydrate at 550 °C through the same process) were carried out with the optimal reaction parameters determined in Example 2. After each transesterification reaction ended, first, the product and the catalyst were separated by centrifugation; then, the catalyst was washed with n - hexane to remove the adsorbed grease on its surface; finally, the catalyst was placed in a vacuum drying oven and dried at 110 °C before being put into the next use. The biodiesel yield obtained in the first use was 91.8%, and the yield decreased to 70.8% after being reused 3 times. The reusability of the attapulgite - modified calcium - based solid catalyst was significantly improved compared with that of pure CaO.

[0058] Table 1 Reusability of attapulgite - modified calcium - based solid catalyst

[0059] Catalyst characterization XRD characterizations were carried out on the catalysts obtained by calcining at different temperatures in Example 1 and Comparative Example 6 and the attapulgite before and after acid treatment, and the Figure 2 results were obtained.

[0060] Figure 2Diffraction peaks of CaO can be seen at 37.45° and 54.00° (ICDD-75-0264), diffraction peaks of Al2Si2O5(OH)4 are at 20.07° and 35.02° (ICDD-75-0857), the corresponding diffraction peaks at 20.86° and 26.64° correspond to SiO2 (ICDD-65-0466), and the diffraction peak at 30.97° is for CaMg(CO3)2 (ICDD-75-1655). It is worth noting that diffraction peaks of Ca2SiO4 can be seen at 31.87°, 32.16° and 41.88° (ICDD-73-2091), and a diffraction peak of Ca(AlSiO4)2 can be seen at 24.51° (ICDD-33-0137), which proves that CaO and the carrier are well combined at 550 °C, while the diffraction peak of Ca(AlSiO4)2 disappears at 600 °C. At 500 °C, strong diffraction peaks of Ca(NO3)2 can be observed at 20.23°, 26.19°, 28.75°, 33.31°, 35.38°, 39.28°, 41.11°, 47.83°, 50.95°, 52.45°, 59.56°, 66.17°, 69.99°, 73.69° (ICDD-07-0204), indicating that calcium nitrate does not decompose into CaO at 500 °C.

[0061] The catalysts obtained by calcining at different temperatures in Example 1 and Comparative Example 6, attapulgite before and after acid treatment, and CaO prepared by the impregnation method were respectively subjected to N2 adsorption experiments to obtain Figure 3 the results of (a)-(d).

[0062] After attapulgite is acid-treated, its specific surface area can be increased from 102.7 m 2 / g to 256.2 m 2 / g, and the pore size distribution in the mesopore range of 2-10 nm is also significantly improved. Such high specific surface area and suitable pore size distribution characteristics make acid-treated attapulgite have application value as a catalyst support. Comparing CaO and attapulgite-modified calcium-based solid catalysts prepared at different calcination temperatures, it is found that the specific surface area is the highest at the calcination temperature of 550 °C, and the pore size distribution is mainly concentrated in 2-100 nm. The coexisting mesopore and macropore structures are beneficial to the mass transfer and diffusion of transesterification reactant molecules.

[0063] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a calcium-based solid catalyst, characterized in that, It includes the following steps: S1. Acid-treat the original attapulgite clay, filter, wash, and dry it to obtain the acid-treated attapulgite clay; S2. Impregnation: Impregnate the acid-treated attapulgite clay with a calcium nitrate solution to obtain a catalyst precursor; S3. Calcination: Calcine and activate the catalyst precursor to obtain a calcium-based solid catalyst; In step S3, the calcination temperature is 550°C - 600°C, and the calcination time is 1.5 - 2.5 h.

2. The preparation method according to claim 1, characterized in that, In step S1, the acid is any one of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, dilute phosphoric acid, and dilute acetic acid; the concentration of the acid solution is 2 - 4 mol / L.

3. The preparation method according to claim 1, wherein In step S1, the acid treatment temperature is 80 - 100°C, and the time is 3 - 4 h; the solid-liquid ratio of the original attapulgite clay to the acid mixture is 0.1 - 0.15 g / mL.

4. The preparation method according to claim 1, wherein In step S2, the mass ratio of calcium oxide prepared after calcination of calcium nitrate to the acid-treated attapulgite clay is 1.7 - 2.1:

1.

5. The preparation method according to claim 1, characterized in that, In step S2, the impregnation temperature is 80 - 100°C, and the time is 3 - 5 h.

6. A calcium-based solid catalyst prepared by the method according to any one of claims 1 - 5.

7. A method for producing biodiesel using the calcium-based solid catalyst according to claim 6, characterized in that, The specific steps are as follows: The alcohol and oil mixture undergoes a transesterification reaction under the catalysis of the above-mentioned calcium-based solid catalyst. The molar ratio of alcohol to oil is 10:1 - 15:1, the addition amount of the catalyst is 3% - 7% of the mass of the oil, the reaction temperature is 50 - 70°C, and the reaction time is 1 - 2 h. After the reaction, the mixture is separated to separate the catalyst and the crude biodiesel.

8. The method according to claim 7, wherein The oil is selected from any one of palm oil, soybean oil, and castor oil; the alcohol is selected from methanol or ethanol.

9. The method according to claim 7, wherein The molar ratio of alcohol to oil is 12:1 - 15:1, the addition amount of the catalyst is 5% - 7% of the mass of the oil, the reaction temperature is 65 - 70°C, and the reaction time is 1.5 - 2 h.

10. The method according to claim 7, characterized in that, After the transesterification reaction, the product and the catalyst are separated by centrifugation, and the catalyst is recovered for reuse.

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